1. Field of the Invention
The present invention relates generally to web printing presses and more particularly to a folder for a web printing press as well as to a method for cutting a web and diverting the resultant signatures into two streams.
2. Background Information
Web printing presses print a continuous web of material, such as paper. The continuous web then is cut in a cutting unit so as to form signatures which can then be folded in a folder or arranged in different manners. In order to arrange signatures in a desired fashion or to permit desired folds, the signatures often may be diverted into two streams, for example, and also may be decelerated. In order to decrease the signature length, it is often necessary to increase the angular velocity ratio between the folder and the printing units of the printing press. As a result, the velocity of the signature has to increase after it is cut from the web, which is counterproductive to downstream transport functions. Signatures thus often must be decelerated in a deceleration device. However, these deceleration devices often damage the signatures, e.g. through dog-earing, or jam the folder because the transfer from or to the deceleration device fails.
U.S. Pat. No. 5,865,082 discloses an apparatus for forming signatures from a web of material. A pair of rotating cylinders cuts the web to form signatures. A plurality of conveying elements traveling in two loops holds the web as the web passes between the cutting cylinders. The conveying elements thus also hold the signatures as they are formed. This device has the disadvantage that the cutting cylinders merely rotate so that the angular velocity ratio of the folder must be increased to decrease signature length.
U.S. Pat. No. 5,740,900 discloses an apparatus for splitting a product stream into an A stream and a B stream. The signatures are gripped by grippers, and alternating grippers rotate to split the product stream. No cutting device is discussed.
An object of the present invention is to provide a reliable device and method for cutting a web into signatures, while permitting for variable-length formats. An alternate or additional object of the present invention is to reliably split the signatures into two streams.
The present invention provides a device for cutting a web of material. The web has a web velocity and moving in a web direction. The device includes a plurality of linearly movable cutting elements capable of moving in the same direction as the web direction for cutting the web into signatures and a plurality of gripper elements interacting with the cutting elements. Since the cutting elements are linearly movable in the web direction, the spacing between the elements can be used to set the signature length. The velocity of the web in the folder advantageously need not be altered in order to change the signature length.
Each gripper element may include a gripper which can then grip the signature and be decelerated, if desired. Each cutting element may include a knife, and each gripper each gripper element may include an anvil against which the knife may cut the web. Each gripper element may also include a retractable sideways-extending pin. The device may further include a deceleration disk interacting with the pin, so that the gripper elements are supported and decelerated by the deceleration disk.
The device also may include a positive drive mechanism for moving the cutting elements in the web direction.
The present invention also provides a device for cutting a web of material including a plurality of linearly movable first cutting elements for moving along a first path, a plurality of linearly movable first gripping elements for moving along the first path, a plurality of linearly movable second cutting elements for moving along a second path and interacting with the first gripping elements, and a plurality of second gripper elements for moving along the second path and interacting with the first cutting elements. The web passes between the first path and the second path in a signature formation area.
Preferably, the first cutting elements and the first gripping elements are arranged in an alternating fashion along the first path. After the signature formation area, the first gripping elements move in a direction opposite the second gripping elements so that an A/B signature split may be achieved.
The first path and the second paths preferably are closed loops.
The cutting elements preferably include a double-bladed laterally-traversing rotary-type knife, which cuts a strip of material between each signatures. This type of knife aids in print quality, since with a single blade knife if there are any imperfections in the cut or the printing, the color from one signature may appear at the edge of the next signature. The strip of material created by the double-bladed knife can remove these imperfections. The device may include a blower and/or suction device to remove the strip of material from the anvil, where the strip becomes attached after cutting.
The present invention also provides a method for cutting a web. A plurality of cutting elements are moved linearly within a signature formation area, with the cutting elements and the web moving in the same direction. As defined herein, xe2x80x9clinearly movingxe2x80x9d or xe2x80x9clinearly movablexe2x80x9d means that the elements can move translationally, as opposed to rotationally as with conventional cutting cylinders. The web is cut with the plurality of cutting elements so as to form signatures. The signature length is varied based on a spacing between the cutting elements within the signature formation area.
The method may further comprise diverting the signatures in an alternating fashion to define a first stream and a second stream of the signatures.
The cutting elements may be moved at the web velocity within the signature formation area.
The method further may include decelerating the signatures after the signatures exit the signature formation area and accelerating the cutting elements before the cutting elements enter the signature formation area.
The method also preferably includes cutting a strip of material between each signature. This cutting step may be performed, for example, by a laterally traversing double-bladed rotary type knife. The strip may then be removed, for example, by a blower or suction device. By eliminating a strip between the signatures, print quality of at the edges of the signatures can be improved.